How are Na and K permeabilities related?

How does tetrodotoxin affect the cell?

Describe an AP.

1-at resting membrane potential (high K conductance, low Na conductance); 2-upstroke of AP (inward current spreads from neighboring APs and causes a depolarization of the cell to threshold -> voltage-gated Na channels open [activation gates] and Na conductance increases = inward Na current and more Na permeability so membrane potential gets near Na equilibrium); 3-repolarization (depolarization causes Na inactivation gates to close slowly and terminate the upstroke, depolarization causes K channels to open and increases K conductance = outward K current and repolarization); 4-hyperpolarizing undershoot (K conductance is higher than at rest so membrane potential approaches K equilibrium more so than at rest but then K conductance returns to normal level and cell goes back to resting potential)

What is responsible for the upstroke of the AP in nerve and skeletal muscle?

Why are refractory periods important?

What is the mechanism of relative refractory periods?

High K permeability makes it difficult to depolarize and elicit another AP (keeps the membrane close to hyperpolarization so need a supramaximal stimulation to generate another AP); Na inactivation gates are open so another AP can be generated

How many alpha helices make a domain in Na, Ca and K channels?

How many domains do Na and Ca channels have?

How many domains does K channel have?

When do the Na activation and inactivation gates open/close?

Activation gates are voltage-dependent so open when membrane reaches threshold; inactivation gates open at peak of AP since are activated by depolarization too but are slower so take longer to respond to depolarization

How do members of the -caine family (lidocaine, etc) work as a local anesthetic?

Explain how local anesthetics get into the cell.

Most are in an unionized form to get across the membrane then gain a proton and become active and unable to get out of membrane; goes to block Na pore then (these drugs are pH dependent and the pH determines whether will get a proton or not)

What are properties of a block due to a local anesthetic?

1-AP amplitude decreases; 2-conduction slows; 3-voltage-dependent (during AP, inside becomes more + so membrane wants to push out molecules with a + charge [the -caine molecule stuck in the pore] but since the drug is there it's stuck and no Na+ can get in the cell); 4-use-dependent (during AP, cell pushes out drug more but it blocked -- injured cells send out more APs but are blocked); 5-pH-dependent (that's how drug can gain/not gain a proton); 6-reversible

What is electrotonic conduction?

What is AP conduction?

Long distance conduction of electrical signals; PROPAGATE in a non-decremental fashion due to voltage-gated Na channels that open with threshold depolarization; ALL OR NONE; region of depolarization moves down axon and resting potential is re-established behind it by Na/K pump